LV25700PM Datasheet, PDF (29/68 Pages) Sanyo Semicon Device – For Car Radio Single chip Tuner IC

LV25700PM
FM Noise cancellar
FM noise canceller detection is performed using two systems (Pin 57 (S-meter AC), Pin 59 (NC IN)) as a
countermeasure against operation errors due to the weak electric field NC sensitivity setting. The detection path is
switched according to the electric field by the S-meter (DC) (Pin 44). FM NC operation can be monitored by the Pin
24 trigger out.
Electric field strength (weak to medium)
Pin 57 (S-meter AC) detection:
ON
Pin 59 (CN IN):
OFF
Medium to strong
ON
ON
C48
1μF
DETOUT
NC_IN
60 59
10.7M
CF
MIX2
FM/AM
DET
Zin=50k
LPF
(for signal delay)
10.7M
Limmit AMP
Vsm
Current output
COPM
HPF
Pilot-Cancel
(CR, primary) (from MPX block)
BUFF
+
-
27kΩ
HPF
(CR, primary)
fc=100kHz
ATT
COPM
+
Noise
Noise
-
AMP
Det
Noise
AGC
6kΩ 60kΩ
27kΩ
SA10
AC Smeter SW
24
BUFF
NC_HOLD
TO MPX
DC-
Moni
Gate time
control (FM)
COPM
+
-
NC
STOP
Gate time
control (AM)
SA24
FORCENOAGC _SA19
AM NC STOP
SA19
Noise_Sens_MAIN
SA20
AM NC Gate Time
44
S-Meter
57
AC S-Meter
47
Noise AGC
Description of FM NC functions
SA : D
Recommended Setting
SA24
D2
Nose-AGC Th.
Forced noise AGC
[1]Force
Noise AGC
SA18
D6-D7
SA10
D1
Noise-Sens.
NC load switching
AC S-Meter
NC sensitivity switching
(Fixed to normal)
[0]
15kΩ
[0]
54kΩ
SA09
NC SENS MAIN
[18]
D0-D4 Adjusting the NC noise
detection sensitivity
Description of Functions
0: Fixes the noise detection sensitivity.
1: Uses noise AGC in the forcibly applied state.
The noise detection sensitivity can be adjusted by DAC (SA09, D0 to D4) control.
The noise detection sensitivity is adjusted by switching the noise amplifier output
load.
Reduces the AC-S-meter internal load resistance value by approximately half.
(54kΩ//60kΩ → 27kΩ//60kΩ)
0: Normal (Internal load = 54kΩ//60kΩ)
1: ON (Internal load = 27kΩ//60kΩ)
However, note that in FM mode the MRC and IF filter also operate by detecting
the AC component of the same pin (AC_Vsm), so these functions are affected by
this bit.
This is valid only in reception mode.
However, it is invalid when SA24 D2 is set to OFF (normal).
When SA24 D2 is ON
Increasing the DAC setting increases the comparator threshold voltage, and
worsens the noise detection sensitivity.
Conversely, reducing the DAC setting enhances the detection sensitivity.
(However, reducing the DAC setting by too much increases the chances of
operation errors.)
No.A1709-29/68